The insectan nervous system evolved from the segmented system of annelid worms,
such as the earthworm. Each of the insect's segments has its own nerve center,
called a ganglion, which is connected by a pair of nerves to the ganglia of
the adjacent segments. The insect's head consists of a set of fused segments;
if you look closely at the head capsule of a grasshopper you can see some of
the sutures between the segments. Inside the head, the segmental ganglia have
fused to form a brain. The major parts of an insect's brain are the:
- optic lobes, which provide a link between the receptor surfaces of the
eyes and the brain. The optic lobes perform the first steps in interpreting
visual information for the insect.
- ocelli (singular = ocellus), accessory eyes which are important in perceiving
the intensity of illumination. Many insects have three, while some have only
two, or even none.
- the antennal lobes, the mushroom bodies. The antennal lobes receive input
from millions of olfactory receptors and reduce it to manageable taste and
- mushroom bodies. If an insect "thinks" this is where it happens.
These are the "higher" centers in the insect brain, where learning,
memory, and integration occur.
- neurosecretory cells. Peptide hormones produced by the neuroscretory cells
regulate endocrine and homeostatic functions in insects. These cells are analogous
to the hypothalamus of the vertebrate brain.
- corpora cardiaca and corpora allata. Analogous to the pituitary in vertebrates,
these organs secrete hormones into the circulation. The corpora allata produce
juvenile hormone, which plays a critical
role in the regulation of behavior in many insects.
- suboesophageal ganglion. The input for this structure comes from the insect's
mouthparts; this ganglion coordinates the action of the mouthparts when the
copyright ©2002 Michael D. Breed, all rights reserved